types: reserve "ignored" type

Change-Id: I93651245ca4d80c6466ab1aa4f53254a95c4679f
diff --git a/types.rst b/types.rst
index ded24c7..7511dfd 100644
--- a/types.rst
+++ b/types.rst
@@ -138,6 +138,8 @@
 +----------------+-----------------------------------------------------------+
 | 31             | Reserved, formerly *Delegation*                           |
 +----------------+-----------------------------------------------------------+
+| 126            | Reserved, TLV element must be *ignored* during processing |
++----------------+-----------------------------------------------------------+
 | [80, 100]      | Reserved for assignments related to local-link data       |
 |                | processing, e.g., NDNLP_ (1-byte encoding)                |
 +----------------+-----------------------------------------------------------+